(1) Field of the Invention
The present invention relates to a fiber-reinforced polymer molded body and a process for the preparation thereof.
More particularly, the present invention relates to a fiber-reinforced polymer molded body comprising a polymer matrix and a reinforcing layer of a molecularly oriented and silane-crosslinked ultra-high-molecular-weight polyethylene fiber laminated with or embedded in the polymer matrix, which has excellent mechanical characteristics such as high elastic modulus and high strength and excellent electric characteristics, and a process for the preparation of this molded body.
(2) Description of the Prior Art
Japanese patent application Laid-Open Specification No. 171951/83 discloses a composite structure comprising a network of a ultra-high-molecular-weight polyethylene fiber or polypropylene fiber and a matrix composed of a polymer having a polyethylene crystal region or polypropylene crystal region and having a melting point or sticking point lower by at least 3.degree. C. than the melting point of the polyolefin fiber. It is taught that this composite structure has a practically measured strength higher than the theoretically estimated value of the strength and this increase of the strength in the composite structure may be due to a certain desirable action outweighing the loss of the crystallinity of the fiber caused at the molding step.
A drawn fiber of ultra-high-molecular-weight polyethylene has high elastic modulus and high tensile strength but it still retains an inherent defect of polyethylene, that is, a poor heat resistance.
It is known that the heat resistance of polyethylene is generally improved by molecular orientation or crosslinking of polyethylene. However, the improvement of the heat resistance in this conventional technique is limited, and it is impossible to overcome the inherent restriction of polyethylene, that is, a relatively low melting point of 110.degree. to 140.degree. C. So far as we know, when molded bodies of polyethylene are exposed to a temperature of 180.degree. C. for 10 minutes, most of them are fused and the strength is lost.
Accordingly, a fiber-reinforced polymer composite structure formed by combining a polyolefin fiber with a polymer matrix at a temperature higher than the melting point of the polyolefin fiber, in which the polyolefin fiber is present while retaining the inherent orientation and crystallization state has not been known.